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- ItemInvestigating the Mutagenicity of a Cold Argon-Plasma Jet in an HET-MN Model(San Francisco, California, US : PLOS, 2016) Kluge, Susanne; Bekeschus, Sander; Bender, Claudia; Benkhai, Hicham; Sckell, Axel; Below, Harald; Stope, Matthias B.; Kramer, Axel; Yousfi, MohammedObjective: So-called cold physical plasmas for biomedical applications generate reactive oxygen and nitrogen species and the latter can trigger DNA damage at high concentrations. Therefore, the mutagenic risks of a certified atmospheric pressure argon plasma jet (kINPen MED) and its predecessor model (kINPen 09) were assessed. Methods: Inner egg membranes of fertilized chicken eggs received a single treatment with either the kINPen 09 (1.5, 2.0, or 2.5 min) or the kINPen MED (3, 4, 5, or 10 min). After three days of incubation, blood smears (panoptic May-Grünwald-Giemsa stain) were performed, and 1000 erythrocytes per egg were evaluated for the presence of polychromatic and normochromic nuclear staining as well as nuclear aberrations and binucleated cells (hen’s egg test for micronuclei induction, HET-MN). At the same time, the embryo mortality was documented. For each experiment, positive controls (cyclophosphamide and methotrexate) and negative controls (NaCl-solution, argon gas) were included. Additionally, the antioxidant potential of the blood plasma was assessed by ascorbic acid oxidation assay after treatment. Results: For both plasma sources, there was no evidence of genotoxicity, although at the longest plasma exposure time of 10 min the mortality of the embryos exceeded 40%. The antioxidant potential in the egg’s blood plasma was not significantly reduced immediately (p = 0.32) or 1 h (p = 0.19) post exposure to cold plasma. Conclusion: The longest plasma treatment time with the kINPen MED was 5–10 fold above the recommended limit for treatment of chronic wounds in clinics. We did not find mutagenic effects for any plasma treatment time using the either kINPen 09 or kINPen MED. The data provided with the current study seem to confirm the lack of a genotoxic potential suggesting that a veterinary or clinical application of these argon plasma jets does not pose mutagenic risks.
- ItemHydrogen peroxide production of underwater nanosecond-pulsed streamer discharges with respect to pulse parameters and associated discharge characteristics(Bristol : IOP Publ., 2022) Rataj, Raphael; Werneburg, Matthias; Below, Harald; Kolb, Juergen F.Abstract Pulsed streamer discharges submerged in water have demonstrated potential in a number of applications. Especially the generation of discharges by short high-voltage pulses in the nanosecond range has been found to offer advantages with respect to efficacies and efficiencies. The exploited plasma chemistry generally relies on the initial production of short-lived species, e.g. hydroxyl radicals. Since the diagnostic of these transient species is not readily possible, a quantification of hydrogen peroxide provides an adequate assessment of underlying reactions. These conceivably depend on the characteristics of the high-voltage pulses, such as pulse duration, pulse amplitude, as well as pulse steepness. A novel electrochemical flow-injection system was used to relate these parameters to hydrogen peroxide concentrations. Accordingly, the accumulated hydrogen peroxide production for streamer discharges ignited in deionized water was investigated for pulse durations of 100 ns and 300 ns, pulse amplitudes between 54 kV and 64 kV, and pulse rise times from 16 ns to 31 ns. An independent control of the individual pulse parameters was enabled by providing the high-voltage pulses with a Blumlein line. Applied voltage, discharge current, optical light emission and time-integrated images were recorded for each individual discharge to determine dissipated energy, inception statistic, discharge expansion and the lifetime of a discharge. Pulse steepness did not affect the hydrogen peroxide production rate, but an increase in amplitude of 10 kV for 100 ns pulses nearly doubled the rate to (0.19 ± 0.01) mol l−1 s−1, which was overall the highest determined rate. The energy efficiency did not change with pulse amplitude, but was sensitive to pulse duration. Notably, production rate and efficiency doubled when the pulse duration decreased from 300 ns to 100 ns, resulting in the best peroxide production efficiency of (9.2 ± 0.9) g kWh−1. The detailed analysis revealed that the hydrogen peroxide production rate could be described by the energy dissipation in a representative single streamer. The production efficiency was affected by the corresponding discharge volume, which was comprised by the collective volume of all filaments. Hence, dissipating more energy in a filament resulted in an increased production rate, while increasing the relative volume of the discharge compared to its propagation time increased the energy efficiency.
- ItemThe Effect of Plasma Treated Water Unit Processes on the Food Quality Characteristics of Fresh-Cut Endive(Lausanne : Frontiers Media, 2021-1-27) Schnabel, Uta; Handorf, Oliver; Winter, Hauke; Weihe, Thomas; Weit, Christoph; Schäfer, Jan; Stachowiak, Jörg; Boehm, Daniela; Below, Harald; Bourke, Paula; Ehlbeck, JörgThis study evaluated the impact of a defined plasma treated water (PTW) when applied to various stages within fresh-cut endive processing. The quality characteristic responses were investigated to establish the impact of the PTW unit processes and where PTW may be optimally applied in a model process line to retain or improve produce quality. Different stages of application of PTW within the washing process were investigated and compared to tap water and chlorine dioxide. Fresh-cut endive (Cichorium endivia L.) samples were analyzed for retention of food quality characteristics. Measurements included color, texture, and nitrate quantification. Effects on tissue surface and cell organelles were observed through scanning electron and atomic force microscopy. Overall, the endive quality characteristics were retained by incorporating PTW in the washing process. Furthermore, promising results for color and texture characteristics were observed, which were supported by the microscopic assays of the vegetal tissue. While ion chromatography detected high concentrations of nitrite and nitrate in PTW, these did not affect the nitrate concentration of the lettuce tissue post-processing and were below the concentrations within EU regulations. These results provide a pathway to scale up the industrial application of PTW to improve and retain quality characteristic retention of fresh leafy products, whilst also harnessing the plasma functionalized water as a process intervention for reducing microbial load at multiple points, whether on the food surface, within the process water or on food-processing surfaces.
- ItemPlasma-treated air and water-assessment of synergistic antimicrobial effects for sanitation of food processing surfaces and environment(Basel : MDPI, 2019) Schnabel, Uta; Handorf, Oliver; Yarova, Kateryna; Zessin, Björn; Zechlin, Susann; Sydow, Diana; Zellmer, Elke; Stachowiak, Jörg; Andrasch, Mathias; Below, Harald; Ehlbeck, JörgThe synergistic antimicrobial effects of plasma-processed air (PPA) and plasma-treated water (PTW), which are indirectly generated by a microwave-induced non-atmospheric pressure plasma, were investigated with the aid of proliferation assays. For this purpose, microorganisms (Listeria monocytogenes, Escherichia coli, Pectobacterium carotovorum, sporulated Bacillus atrophaeus) were cultivated as monocultures on specimens with polymeric surface structures. Both the distinct and synergistic antimicrobial potential of PPA and PTW were governed by the plasma-on time (5–50 s) and the treatment time of the specimens with PPA/PTW (1–5 min). In single PTW treatment of the bacteria, an elevation of the reduction factor with increasing treatment time could be observed (e.g., reduction factor of 2.4 to 3.0 for P. carotovorum). In comparison, the combination of PTW and subsequent PPA treatment leads to synergistic effects that are clearly not induced by longer treatment times. These findings have been valid for all bacteria (L. monocytogenes > P. carotovorum = E. coli). Controversially, the effect is reversed for endospores of B. atrophaeus. With pure PPA treatment, a strong inactivation at 50 s plasma-on time is detectable, whereas single PTW treatment shows no effect even with increasing treatment parameters. The use of synergistic effects of PTW for cleaning and PPA for drying shows a clear alternative for currently used sanitation methods in production plants. Highlights: Non-thermal atmospheric pressure microwave plasma source used indirect in two different modes—gaseous and liquid; Measurement of short and long-living nitrite and nitrate in corrosive gas PPA (plasma-processed air) and complex liquid PTW (plasma-treated water); Application of PTW and PPA in single and combined use for biological decontamination of different microorganisms.
- ItemPlasma-Functionalized Water: from Bench to Prototype for Fresh-Cut Lettuce(New York : Springer, 2020) Schnabel, Uta; Handorf, Oliver; Stachowiak, Joerg; Boehm, Daniela; Weit, Christoph; Weihe, Thomas; Schäfer, Jan; Below, Harald; Bourke, Paula; Ehlbeck, JoergFresh-cut produce like lettuce may contain a very high microbial load, including human pathogens. Therefore, the need for antimicrobial agents at post-harvest stages to mitigate microbial cross-contamination and growth is evident. Sanitation based on non-thermal plasma (NTP) reveals innovative food processing possibilities by application at different points along the food chain, for production, modification, and preservation, as well as in packaging of plant- and animal-based food. The aim of the present study was to evaluate the applicability of plasma-treated water (PTW) as antimicrobial process water additives for washing in fresh-cut lettuce processing. Antibacterial activities of PTW the natural occurring microflora of lettuce were examined. Different process variants of PTW application inside the washing process were investigated. Fresh-cut lettuce were investigated regarding microbiological safety and food quality. Samples were analyzed for antimicrobial and metabolic activity as well as metabolic vitality to prove food safety. The investigations for food quality included color and texture analyses and nitrate concentration detection in fresh tissue as well as microscopic measurements by scanning electron microscopy (SEM) and atomic force microscopy (AFM) for tissue surface structure and transmission electron microscopy (TEM) for cell organelle investigations. The application of PTW allowed up to 5 log10 cycle reduction, depending on the process variant and scale (lab and pilot scale). The increase of antimicrobial activity was accompanied by a reduction of metabolic activity, but not consequently by a decrease in metabolic vitality. Food quality was not affected by the use of PTW in the washing process of the fresh-cut lettuce. The promising results in color and texture were supported by the results of the microscopic assays. These promising results may lead to an industrial application of PTW as process water additive in fresh-cut produce processing to reduce the microbial load on the food surface and in addition in the process water or on food processing surfaces. © 2020, The Author(s).